1. Field of the Invention
The present invention relates to an image detecting apparatus, and more particularly, relates to an image detecting apparatus for good imaging quality.
2. Description of the Prior Art
FIG. 1 is schematic view of a conventional image detecting apparatus, and FIG. 2 is a schematic view of a light beam in a sensing system of the conventional image detecting apparatus. Referring to FIGS. 1 and 2, the conventional image detecting apparatus 100 comprises an illumination system 110 and a sensing system 120. The illumination system 110 comprises a light source 112 and a lens 114, wherein the light source 112 is for providing a light beam 113, and the lens 114 is disposed on a transmission path of the light beam 113 for focusing the light beam 113 on a working surface 50. The light beam 113 has an optical axis 113a, and in FIG. 1, the optical axis 113a is represented the light beam 113. The sensing system 120 comprises a sensing unit 122 and a lens 124. The sensing unit 122 and the lens 124 are disposed on the transmission path of the light beam 113 reflected by the working surface 50, and the lens 124 is disposed between the sensing unit 122 and the working surface 50 for focusing the light beam 113 on the sensing unit 122.
In the conventional sensing system 120, the optical axis 124b of the lens 124 overlaps the optical axis 113a of the light beam 113. The lens 124 is for focusing the light beam 113 on the sensing unit 122. However, in the conventional technique, optical path differences of light rays of the light beam 113 between the working surface 50 and the sensing unit 122 are obviously different. Take main light rays (i.e. light rays with high intensity) 113b, 113c as an example, the transmission path of the light ray 113c is obviously longer than that of the light ray 113b, and thus the imaging quality is reduced.
FIG. 3 shows simulated transmission paths, simulated by an optical simulation software, of light rays of the light beam 113 in the conventional sensing system 120. Referring to FIG. 3, in the conventional sensing system 120, the light beam 113 can not be exactly focused on the sensing unit 122. Therefore, a distortion is occurred and the imaging quality is consequentially reduced.